This invention relates to a RESINATED CAPACITIVE-BODY CAPACITOR WITH INTERSPACE AND EXPLOSION-PREVENTING DEVICE.
This invention finds peculiar and convenient application to capacitors equipped with explosion-preventing devices by a pressure activated fuse or disconnecting device enclosed in an encasing plastic shell.
In the present state of the art, explosion-preventing devices are well-known and consist of a pressure-activated movable part in their cover. At pressure increase, when, for example, owing to a short circuit inside the capacitor, a certain amount of gas is produced, and said movable part goes away from the capacitive body, snatching the respective electric conductors wires switching off the electric circuit. In this way the danger of bursting of the capacitor is avoided. In these solutions the capacitive body is in air freely or in oil encased in the respective encasing shell. Reference is made to the Standard Elektrik Lorenz AG Stuttgart--German Patent Disclosure "Auslegeschrift" No. 2348483 filed on Sept. 26 1973 and published on Apr. 10 1975.
Resinated capacitors so called "dry capacitors" are known where the solidified (hardened) resin encloses in a whole all its capacitive body and its container and a movable part disconnecting device (explosion-preventing device) in its cap or cover. These capacitors have the resin welded to the respective casing shell and when a short circuit raises far from the explosion-preventing device, it cannot react on said explosion-preventing device because the pressure increase remains encased between the capacitive body and the corresponding container in that far area, so that the explosion cannot be avoided.
The same Assignee of the Applicant in a copending Giorgio Lamma et al. U.S. patent application has suggested some solutions in order to avoid this drawback. In this patent application is suggested the utilization of an extremely thin shell that contains the capacitive body and its solidified resin in order to realize a preassembled. This preassembled shall be inserted in the respective container or encasing shell, being the first one smaller in diameter and length than the second one realizing an air interspace chamber around the capacitive body between the two respective shells. This air interspace chamber is realized by spacers in said interspace chamber. However, this solution is very expensive and involves greater processing phases, so that the cost of this capacitor cannot be competitive with the traditional solutions needing two encasing shells.
This invention as claimed is intended to remedy these drawbacks. Concerning the respective anti-explosion device by pressure activable fuse, other solutions designed in plastic material utilize a cover provided with an "annular baffle" with the electric connections fixed to it. At pressure increase it moves outwards, snatching the electric connections and switching off the electric circuit in order to carry out the over-pressure protecting function. In these solutions further drawbacks occur because the action of taking away the electric connection portion in order to snatch away the electric conductors (bellows or baffle) not always results in the switching off of said connections for example, owing to their unforseen extension or greater resistance to traction; reaction times are further lengthened so that when the over-pressure protection intervenes the damage is at this point irreparable, since the switching off occurred too late.
For this purpose, intermediate-diaphragm solutions have been suggested. These are placed inside under the respective cap or cover and fixed to the capacitor structure or capacitive body, aiding in snatching the electrical conductors electrically connected under it. This solution is disclosed in Ernst U.S. Pat. No. 3,473,088 patented Oct. 14, 1969 "PRESSURE-ACTIVATED FUSE FOR ELECTRICAL COMPONENTS" and Netherwood No. U.S. Pat. No. 3,553,542 patented Jan. 5, 1971. Other similar solutions are suggested in French patent application Disclosure No. 2313757 patent application No. 7616853 filing date Mar. 6, 1976 in the name of BICC LIMITED GB.
This invention as claimed is further intended to guarantee a safe and immediate switching off of the electric connections, also with low pressure increases in incipient heating phase due to possible short-circuit by the use of a diaphragm according to the above-mentioned principle. Moreover, the invention as claimed is intended to carry out a very cheap and functional capacitor, being its entire encasing frame realized in plastic material without preventing thus the greatest functionality and reliability particularly with reference to antiburst effects.